(1) Field of the Invention
The present invention relates to a porous ceramic material and a process for the preparation thereof. More particularly, it relates to a porous ceramic material having a multiplicity of pores having a specific size and a multiplicity of capillary void paths having a specific size and connecting the pores to the exterior space of the porous ceramic material, which is valuable as a material for regeneration of bone and other medical purposes and also an electronic material or a genetic engineering material, and processes for the preparation thereof. It also relates to a method of remedying a defect of bone of a human or animal.
(2) Description of the Prior Art
A calcium phosphate compound such as hydroxyapatite or a solid solution thereof has a good compatibility with a living body and is valuable as a medical material such as an osteogenetic material, for example, a substitute or prosthesis for a bone or dental root. For example, Japanese Unexamined Patent Publication No. 56-54841 discloses a filler for a bone defect or antrum, which comprises a calcium phosphate compound powder of the apatite type crystal structure.
Furthermore, Japanese Unexamined Patent Publication No. 56-166843 discloses a filler for a bone defect or antrum, which is composed of a porous body of a calcium phosphate compound. In pores contained in this porous body of the calcium phosphate compound, the maximum pore diameter is 3.00 mm and the minimum pore diameter is 0.05 mm. These pores have such a shape and size that bone-forming components of a living body can easily intrude into these pores. This porous body has a substantially continuous three-dimensional network structure.
These conventional calcium phosphate compounds have problems in that deformation is caused with the lapse of time after a surgical treatment such as filling or prosthesis or hardening is promoted in the soft contact tissue near the filled or embedded portion, whereupon the resulting abnormal tissue must be excised. When remedying of a defect of the hard tissue of a living body caused by excision a bone tumor, bone resorption with age or external damage of a bone, it is most preferred that natural healing be promoted. Substitution or prosthesis by an artificial product is not always preferred. When such an artificial article is filled in a living body or included in a living body by prosthesis, it is most preferred that the artificial product be consumed in the living body in due course and the natural living tissue be regenerated instead to repair the defect. In this case, it is important that the speed of substitution of the artificial article by the living tissue (namely, the turnover speed) should be appropriate. If the turnover speed is excessively high, trouble such as inflammation is caused in the treated portion, resulting in complications, for example, development of cancer. In the case where the turnover speed is low and the artificial article is present in a living body for a long time, deformation of the bone tissue or other living tissues in the treated portion or hardening of the soft tissue near the treated portion is caused, whereupon excision becomes necessary in some cases.
In order to cope with the foregoing problems, it is important that a filler or prosthetic material inserted in a living body satisfy the requirements for induction and substitution of the living body tissue at a cell level. More specifically, it is important to appropriately promote the activation of an osteolytic cell (osteolysis) and an osteoblast to the living body tissue, control intrusion and development of an osteoclast and a collagen fiber promoting hardening of the soft tissue, and also control hardening of the bone tissue and not to inhibit intrusion of erythrocytes and body fluid and development of capillary blood vessels.
In order to satisfy these requirements, it is important that a filler or prosthetic material to be inserted into a living body have good compatibility with the living body, especially good bioresponsibility, should provide a residence propagation space suitable for the activation of desired cells, and should prevent intrusion of undesirable cells and hardening of the bone tissue by abnormal development of a collagen fiber.